That is correct, no contact details can be exchanged before purchase.
This is how a collection item sale works:
You buy the item, and pay through eBay checkout, cash is no longer allowed for collection items. Then, all contact details can be exchanged, and you receive a collection code.
You go and inspect the item, if you do not like it you do not hand over that code, that is the only proof a seller has / needs to show an item was collected. The seller cancels the order citing Buyer requests to cancel, this fully refunds you, and it doesn't affect their seller performance.
I know all of the above sounds long winded, but those are the rules.
@simon270172